Welcome to the forum!
There should be an "Attach files" box on the left, just under the window where you enter the text of your post. [IIRC, it might not show up until you've posted some minimum number of times (?)] Have your cursor in the correct place on your post. Then click the box. Find and choose the photo you want to add. The system will then ask you if you want to include it as thumbnail or full size.
I'd offer help on your original question, but (1) I don't own a Maximat, and (2) wiring here in the US (110V) will be done differently than in the UK (220V). Hope somebody from a "220 volt country" can help you out!